1. Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700032, India
2. Department of Physics, Jadavpur University, Kolkata 700032, India
3. Department of Higher Education, (University Branch) Government of West Bengal, Bikash Bhavan, Salt Lake, Kolkata-91, India
4. School of Chemistry, The University of Reading, P. O. Box 224, Whiteknights, Reading RG6 6AD, UK